Employing multi-antenna transmitting and multi-antenna receiving technique in a wireless communication system can improve transmitting capacity of the communication system by many times theoretically. However, at the receiving end in a multi-antenna wireless communication system, signal interference in space domain (i.e., between antennas) exists. When signal transmission is carried out on a single carrier of wide band or multiple carriers of wide sub-bands, the wireless channel of each carrier becomes a frequency selective channel, i.e., inter-symbol interference in different times exists. Therefore, in a frequency selective channel environment, signal interference between different antennas, signal interference in different times, and Additive White Gaussian Noise (AWGN) exist at the receiving end of the multi-antenna system. At the receiving end, it is necessary to suppress interference signals in space domain and time domain dimensions and additive noise, obtain estimation result of the transmitted signals, and provide hard-decision output in an encoding system without error control; or, in an error control encoding system utilizing soft-decision decoding technique, the soft information must be obtained by means of soft demodulation and then sent to a decoder.
In an environment with inter-symbol interference between antennae and inter-symbol interference in different times, the detecting methods are mainly categorized into two categories: one category is based on maximum a posteriori (MAP) and it's simplified algorithms, which are highly complex; the complexity of the optimal MAP algorithm increase exponentially with the number of transmitting antennae, the number of bits carried in each symbol and the channel memory length; when the number of antennae is large or high order modulation is used, it is difficult to apply such detection methods in actual systems. The other category involves detectors that utilize linear filtering and interference cancellation techniques, which are less complex. Minimum Mean Square Error (MMSE) criterion and Zero-Forcing (ZF) criterion are two commonly used criteria, whose complexity increases in cubic power relationship with the product of channel memory length and number of transmitting antennae. However, the complexity in implementation of such detecting method is still too high when the number of antennae is large or the channel memory length is long. In contrast, the complexity of MF-based interference cancellation detectors increases linearly as product of channel retention length and number of transmitting antennae increases, and therefore is relatively low; however, if the antennae have correlation to some degree between each other, such detectors have poor performance, and even can't work normally in some environments. Therefore, it is of great significance to seek for a high performance detector with lower complexity in implementation in practice. In communication systems, an error control encoding technique is usually used at the transmitting end to improve transmission performance and enhance resistance to fading, noise, and interference. Turbo Code, Low Density Parity Check (LDPC) code, etc., are error control encoding methods with high error correction capability. At the receiving end, utilizing an iterative detection decoding receiver in which the detector works with the decoder in an iterative mode can significantly improve performance, when compared to a traditional receiver in which the detector works with the decoder in a cascade mode. However, an iterative detection decoding receiver requires that the detector must take soft input and provide soft output, i.e., the detector must be able to sue the feedback from the decoder as a priori information and provide soft-decision information to the decoder. It is an important task to seek for a soft-input and soft-output detector that has high performance but low complexity for multi-antenna wireless communication systems in a frequency selective channel environment, in order to support wide application of multi-antenna wireless communication systems.